1. Field of the Invention
This invention relates to a vehicle submergence detection sensor, particularly to a vehicle submergence detection sensor wherein submergence of a vehicle is detected when an electrical conductive state is established between a pair of opposed electrodes installed on a control circuit board in the vehicle which conducts due to water.
2. Description of the Related Art
When an automobile or any other vehicle accidentally falls into the sea, a river, lake or the like, the occupants are likely to have only a short time to escape because a vehicle ordinarily sinks rapidly (quickly becomes submerged).
Efforts have therefore been made to develop systems capable of detecting vehicle submergence by means of an onboard submergence detection sensor and of, upon detection of submergence, immediately implementing measures to avoid danger to the passengers. Japanese Laid-Open Patent Application No. Sho 61(1986)-235,247, for example, depicts a vehicle submergence prevention system that is equipped with a submergence detection sensor which responds to vehicle submergence by activating an air bag to prevent the vehicle from sinking.
The system described in this Publication adopts a configuration including a submergence sensor for detecting what portion of the vehicle has sunk into water, a gas generating means for generating gas in response to a signal from the submergence sensor, and an air bag inflated by gas from the gas generating means to produce buoyancy in the water. This vehicle submergence prevention system utilizes a float-type submergence detection sensor.
This float-type submergence detection sensor is, however, disadvantageous. One drawback is that it requires a complex structure. The sensor""s principle of operation also causes a problem. Specifically, for detecting submergence, it requires a switch to be activated by a float buoyed up by water flowing into a sensor case. As the submergence detection therefore takes time, operations for avoiding danger may be delayed.
A system developed to overcome these problems provides a pair of pad-like electrodes for submergence detection on a control circuit board of a power window control unit that operates a power window (windows powered by electric motor for being opened or closed) in response to a leak in current occurring when the space between the two electrodes has become filled with water. The structure of the submergence detection sensor of this type will be explained with reference to FIGS. 11 and 12. FIG. 11 is a perspective view of the overall structure of the submergence detection sensor and FIG. 12 is a block diagram showing the circuit of the sensor.
As shown in FIG. 11, the submergence detection sensor assigned with reference number 60 is installed on a control circuit board 62 for the power window control unit. Similarly, multi-operation circuits 64, 66 and a connector 70 are installed on the control circuit board 62. The submergence detection sensor 60 includes a pair of pad-like electrodes 68 for submergence detection mounted on the control circuit board 62. The electrode pads 68 are made of a conductive material such as copper and are installed in an opposing relationship with a space therebetween. When the submergence detection sensor 60 detects vehicle submergence, it outputs a signal to a motor of a power window driver (not shown in FIG. 11) through the multi-operation circuits 64, 66 and the connector 70.
More specifically, as shown in FIG. 12, one of the electrodes 68 is grounded and the other is connected to a submergence detection circuit 72 (whose operation is conducted by the multi-operation circuits 64, 66). The submergence detection circuit 72 is connected to a power window output circuit 74 (whose operation is similarly conducted by the multi-operation circuits 64, 66) to enable driving of the motor 76 of the power window.
When water (fresh water or seawater) enters between the electrodes 68, submergence of the vehicle is detected by the submergence detection sensor 60 owing to water establishing an electrically conductive state between the electrodes 68. A leak current therefore flows between the electrodes 68. Upon detecting the leak current, the submergence detection circuit 72 discriminates that the vehicle is in a submerged state and outputs the signal to the power window output circuit 74. In response, the power window output circuit 74 drives the motor 76 to control a danger avoidance operation, e.g., to open the power window.
The submergence detection sensor of this type which has pad-like electrodes for vehicle submergence detection on a control unit circuit board also has problems.
One is that water (dew) condensing between the electrodes owing to temperature difference relative to the outside air and/or high humidity also causes leak current to flow between the electrodes. This sensor is therefore susceptible to false detection, i.e., detection of submergence when the vehicle is not submerged.
Another is that the control unit circuit current promotes migration (intramolecular atom movement) of solder tin, which together with the action of water and the potential difference between the electrodes, produces electrocorrosion that dissolves out the electrode pad copper and establishes a conductive state between the electrodes. This is also a cause of false detection, i.e., detection of submergence when the vehicle is not submerged.
The object of the present invention is therefore to provide a vehicle submergence detection sensor, which while being of the type that detects vehicle submergence from the establishment of electrical conductivity between two electrodes placed in an opposing relationship on a control circuit board by entry of water therebetween, is capable of reliably detecting vehicle submergence, when in fact it submerges in water, without making false detections owing to water condensation on the control circuit board or migration occurring therein.
In accordance with a fist aspect of the present invention, there is provided a submergence detection sensor installed in a vehicle, comprising: a circuit board; a pair of electrodes installed on the circuit board which are electrically conductive upon entry of water to generate a leak current therebetween; a submergence detection circuit connected to the electrodes to receive the leak current and to compare with a threshold value to discriminate whether the vehicle submerges into water; and a slot provided in a gap between the electrodes which penetrates the circuit board such that water present at the gap is discharged from the circuit board.
In accordance with a second aspect of the present invention, there is provided a submergence detection sensor installed in a vehicle, comprising: a circuit board; a pair of electrodes installed on the circuit board which are electrically conductive upon entry of water to generate a leak current therebetween; and a submergence detection circuit connected to the electrodes to receive the leak current and to compare with a threshold value to discriminate whether the vehicle submerges into water; wherein: the electrodes are configured to be bar-like such that resistance is different for a case when they are submerged in water and when they are not submerged in water.